Synthesis and Biological Evaluation of Pyrazolo[1,5-a]-pyrimidine-containing 99mTc Nitrido Radiopharmaceuticals as Imaging Agents for Tumors

The compound 5-((2-aminoethylamino)methyl)-7-(4-bromoanilino)-3-cyano-pyrazolo[1,5-a]pyrimidine (ABCPP) was synthesized and conjugated with N-mercapto-acetylglycine (MAG), N-mercaptoacetylphenylalanine (MAF) and N-mercaptoacetylvaline (MAA), respectively. These three compounds were labeled successfully with [99mTcN]2+ intermediate in high radiochemical purities. Biodistribution in tumor-bearing mice demonstrated that the three new complexes showed tumor accumulation, high tumor-to-muscle (T/M) ratios and fast clearance from blood and muscle. Among them, the 99mTcN-MAG-ABCPP showed the most favorable characteristics, with tumor/blood and tumor/ muscle ratios reaching 1.51 and 2.97 at 30 min post-injection, 1.84 and 2.49 at 60 min post-injection, suggesting it could be further studied as potential tumor imaging agent for single photon emission computed tomography (SPECT).